1. Field of the Invention
The present invention relates to a magnetic field sensing element for detecting a change in a magnetic field, and more particularly, such an element used in a device for detecting the rotation of a magnetic body.
2. Description of the Related Art
Generally, a magnetoresistance element (hereinafter referred to as an MR element) is an element whose resistance changes depending on an angle formed by the direction of magnetization of a ferromagnetic body (Nixe2x80x94Fe or Nixe2x80x94Co, for example) thin film and the direction of an electric current. The resistance of such an MR element is minimum when the direction of an electric current and the direction of magnetization cross at right angles to each other, and is maximum when the angle formed by the direction of an electric current and the direction of magnetization is 0xc2x0, that is, when the directions are the same or completely opposite. Such a change in resistance is referred to as an MR ratio, and is typically 2-3% with respect to Nixe2x80x94Fe and 5-6% with respect to Nixe2x80x94Co.
FIGS. 34 and 35 are a side view and a perspective view, respectively, showing the structure of a conventional magnetic field sensing device.
As shown in FIG. 34, the conventional magnetic field sensing device comprises a rotation axis 41, a magnetic rotating body 42 which has at least one concavity and convexity and which rotates synchronously with the rotation of the rotation axis 41, an MR element 43 arranged with a predetermined gap between itself and the magnetic rotating body 42, a magnet 44 for applying a magnetic field to the MR element 43, and an integrated circuit 45 for processing an output of the MR element 43. The MR element 43 has a magnetoresistance pattern 46 and a thin film surface (magnetic-sensitive surface) 47.
In such a magnetic field sensing device, rotation of the magnetic rotating body 42 causes a change in the magnetic field penetrating the thin film surface 47 which is the magnetic-sensitive surface of the MR element 43, resulting in a change in the resistance of the magnetoresistance pattern 46.
However, since the output level of the MR element as a magnetic field sensing element used in such a magnetic field sensing device is low, the detection can not be highly accurate. In order to solve this problem, a magnetic field sensing element using a giant magnetoresistance element (hereinafter referred to as a GMR element) having a high output level has been recently proposed.
FIG. 36 is a graph showing the characteristics of a conventional GMR element.
The GMR element showing the characteristics in FIG. 36 is a laminated body (Fe/Cr, permalloy/Cu/Co/Cu, Co/Cu, FeCo/Cu) as a so-called artificial lattice film where magnetic layers and non-magnetic layers with thickness of several angstroms to several dozen angstroms are alternately laminated. This is disclosed in an article entitled xe2x80x9cMagnetoresistance Effects of Artificial Lattices,xe2x80x9d Japan Applied Magnetics Society Transactions, Vol. 15, No. 51991, pp. 813-821. The laminated body has a much larger MR effect (MR ratio) than the above-mentioned MR element, and, at the same time, is an element which shows the same change in resistance irrespective of the angle formed by the direction of an external magnetic field and the direction of an electric current.
In order to detect a change in the magnetic field, the GMR element substantially forms a magnetic-sensitive surface. Electrodes are formed at the respective ends of the magnetic-sensitive surface to form a bridge circuit. A constant-voltage and constant-current power source is connected between the two facing electrodes of the bridge circuit. The change in the magnetic field acting on the GMR element is detected by converting a change in the resistance of the GMR element into a change in voltage.
FIGS. 37 and 38 are a side view and a perspective view, respectively, showing the structure of a magnetic field sensing device using a conventional GMR element.
In FIGS. 37 and 38, the magnetic field sensing device comprises a rotation axis 41, a magnetic rotating body 42 as a means for imparting a change to a magnetic field, the body having at least one concavity and convexity and having rotatable synchronously with the rotation of the rotation axis 41, a GMR element 48 arranged with a predetermined gap between the magnetic rotating body 42, a magnet 44 as a magnetic field generating means for applying a magnetic field to the GMR element 48, and an integrated circuit 45 for processing an output of the GMR element 48. The GMR element 48 has a magnetoresistance pattern 49 as a magnetic-sensitive pattern and a thin film surface 50.
In such a magnetic field sensing device, rotation of the magnetic rotating body 42 causes a change in the magnetic field penetrating the thin film surface (magnetic-sensitive surface) 47 of the GMR element 48, resulting in a change in the resistance of the magnetoresistance pattern 49.
FIG. 39 is a block diagram showing the magnetic field sensing device using the conventional GMR element.
FIG. 40 is a block diagram showing the detail of the magnetic field sensing device using the conventional GMR element.
The magnetic field sensing device shown in FIGS. 39 and 40 is arranged with a predetermined gap between the magnetic rotating body 42 and itself, and comprises a Wheatstone bridge circuit 51 using the GMR element 48 to which a magnetic field is applied by the magnet 44, a differential amplification circuit 52 for amplifying the output of the Wheatstone bridge circuit 51, a comparison circuit 53 for comparing the output of the differential amplification circuit 52 with a reference value to output a signal of either xe2x80x9c0xe2x80x9d or xe2x80x9c1,xe2x80x9d and an output circuit 54 that switches in response to the output of the comparison circuit 53.
FIG. 41 shows an example of the structure of a circuit of the magnetic field sensing device using the conventional GMR element.
In FIG. 41, the Wheatstone bridge circuit 51 has on its respective sides GMR elements 48a, 48b, 48c, and 48d, for example, with the GMR elements 48a and 48c being connected with a power source terminal VCC, the GMR elements 48 and 48d being polished, the other ends of the GMR elements 48a and 48b being connected with a connection 55, and the other ends of the GMR elements 48c and 48d being connected with a connection 56.
The connection 55 of the Wheatstone bridge circuit 51 is connected with an inverting input terminal of an amplifier 59 of a differential amplification circuit 58 via a resistor 57. The connection 56 is connected with a non-inverting input terminal of the amplifier 59 via a resistor 60, and is further connected with a voltage dividing circuit 62 for forming a reference voltage based on the voltage supplied from the power source terminal VCC via a resistor 61.
An output terminal of the amplifier 59 is connected with its own inverting input terminal via a resistor 63, and is further connected with an inverting input terminal of a comparison circuit 64. A non-inverting input terminal of the comparison circuit 64 is connected with a voltage dividing circuit 66 for forming a reference voltage based on the voltage supplied from the power source terminal VCC, and is further connected with an output terminal of the comparison circuit 64 via a resistor 67.
An output end of the comparison circuit 64 is connected with a base of a transistor 69 of an output circuit 68. The collector of the transistor 69 is connected with an output terminal of the output circuit 68 and is further connected with the power source terminal VCC via a resistor 71. The emitter of the transistor 69 is polished.
FIG. 42 shows the structure of the conventional magnetic field sensing element.
FIG. 43 is a graph showing operating characteristics of the conventional magnetic field sensing element.
As shown in FIG. 42, the Wheatstone bridge comprises the GMR element 48 (formed of 48a, 48b, 48c, and 48d).
As shown in FIG. 43, rotation of the magnetic rotating body 42 causes a change in the magnetic field supplied to the GMR element 48 (48a to 48d), and output corresponding to the concavities and the convexities of the magnetic rotating body 42 can be obtained at an output end of the differential amplification circuit 58.
The output of the differential amplification circuit 58 is supplied to the comparison circuit 64, compared with the reference value as the comparison level, and converted into a signal of either xe2x80x9c0xe2x80x9d or xe2x80x9c1,xe2x80x9d and the signal is further made into a waveform by the output circuit 68. As a result, as shown in FIG. 43, an output of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d with steep leading and trailing edges can be obtained at the output terminal 70.
However, since the GMR element used in the above-mentioned magnetic field sensing element is very sensitive, it is necessary to, for example, smooth the surface of the underlayer on which the GMR element is formed in order to fully bring out its characteristics. Therefore, it is difficult to, for example, form the GMR element on the same surface the integrated circuit is formed.
This makes it necessary to separately form the GMR element and the integrated circuit and then electrically connect them with each other, which leads to low productivity and high manufacturing costs.
Further, since the output of the comparison circuit depends on the gap between the magnetic rotating body and the magnetic field sensing element, there is a problem in that the so-called gap characteristics are bad.
The present invention is made to solve the problems mentioned above, and therefore an object of the present invention is to provide a magnetic field sensing element with low cost, high productivity, and high detection accuracy, and a magnetic field sensing device using the magnetic field sensing element.
According to an aspect of the present invention, there is provided a magnetic field sensing element comprising, an underlayer formed on a substrate, a giant magnetoresistance element formed on the underlayer for detecting a change in a magnetic field, and an integrated circuit formed on the underlayer for carrying out predetermined arithmetic processing based on a change in a magnetic field detected by the giant magnetoresistance element, wherein the giant magnetoresistance element and the integrated circuit are formed on the same surface.
In a preferred form of the invention, a metal film formed on the underlayer for forming the integrated circuit, which is not in a region for forming the integrated circuit, is patterned to form first wiring for connecting the giant magnetoresistance element and the integrated circuit.
In accordance with another aspect of the present invention, the first wiring are formed by wet etching of the metal film and has a tapered shape in section.
In accordance with a further aspect of the present invention, a first level difference buffer layer is formed on the underlayer in a region for forming the giant magnetoresistance element to decrease a difference in the levels between the surface of the metal film for forming the first wiring and a surface for forming the giant magnetoresistance element, and the giant magnetoresistance element is formed on the first level difference buffer layer.
In a further preferred form of the invention, the first level difference buffer layer is formed of an insulating layer, and the level difference between the first level difference buffer layer and the surface of the metal film for forming the first wiring is sufficiently smaller than the film thickness of the giant magnetoresistance element.
In a still further preferred form of the invention, the first level difference buffer layer is a resist layer or resin layer having fluid characteristics formed by spin coating, and the level difference between the first level difference buffer layer and the surface of the metal film for forming the first wiring is sufficiently smaller than the film thickness of the giant magnetoresistance element.
In accordance with a still further aspect of the invention, for the purpose of forming the giant magnetoresistance element, after a giant magnetoresistance element film is formed on the entire surface of the integrated circuit and the first wiring, a portion of the giant magnetoresistance element film on the first wiring then being removed so that the giant magnetoresistance element film formed on the integrated circuit is left unremoved, a protective film then being formed on the unremoved portion of giant magnetoresistance element film.
In accordance with a yet further aspect of the invention, there is provided a magnetic field sensing element comprising, an integrated circuit, an underlayer, and a metal pad formed on a substrate in the order stated, provided with, a second level difference buffer layer formed on the underlayer and the metal pad to absorb the level difference between the surface of the underlayer and the surface of the metal pad, and a giant magnetoresistance element formed on the second level difference buffer layer.
In a further preferred form of the invention, the second level difference buffer layer has a surface that is smoothed by polishing, and the giant magnetoresistance element is formed on the smoothed surface of the second level difference buffer layer.
In a further preferred form of the invention, the second level difference buffer layer is a resist layer or resin layer having a smoothed surface formed by spin coating and the giant magnetoresistance element is formed on the smoothed surface of the smoothed resist layer or resin layer.
In accordance with a yet further aspect of the invention, there is provided a magnetic field sensing element comprising an underlayer formed on one surface of a substrate, a giant magnetoresistance element formed on the underlayer, for detecting a change in a magnetic field, and an integrated circuit formed on the surface opposite to the surface where the giant magnetoresistance element of the substrate is formed, for carrying out predetermined arithmetic processing based on a change in a magnetic field detected by the giant magnetoresistance element.
In a further preferred form of the invention, an underlayer and a giant magnetoresistance element are further formed on the integrated circuit formed on the other surface of the substrate.
In a further preferred form of the present invention, a film, which is identical with the film composing the giant magnetoresistance element, is formed on the first wiring.
In a further preferred form of the present invention, more than half of the top surface and the side surface of the first wiring is coated with the same film that forms the giant magnetoresistance element.
In accordance with a yet further aspect of the present invention, there is provided a magnetic field sensing element comprising an integrated circuit formed on a substrate and having a capasitor portion, an underlayer formed on the integrated circuit, a second metal layer formed on the underlayer, and a giant magnetoresistance element formed on the capacitor portion of the integrated circuit.
In a further preferred form of the present invention, the giant magnetoresistance element is connected with the integrated circuit through second wiring formed by patterning the second metal layer.
In a further preferred form of the present invention, a film, which is identical with the film composing the giant magnetoresistance element, is formed on the second wiring.
In a further preferred form of the present invention, more than half of the top surface and the side surface of the second wiring is coated with the same film that forms the giant magnetoresistance element.
In a further preferred form of the present invention, the giant magnetoresistance element is connected with the integrated circuit through a bonding wire.
In a further preferred form of the present invention, the giant magnetoresistance element is formed by repeatedly laminating a Fe(x)Co(1xe2x88x92x) layer (0xe2x89xa6xxe2x89xa60.3) and a Cu layer, film thickness of the Cu layers per layer being set to such a film thickness that causes the change rate of magnetoresistance in a layer of the Cu layers to be around the second peak, and protective films on the giant magnetoresistance element is formed by spin coating or by means of low-thermal plasma CVD method.
In a further preferred form of the present invention, a diode is formed between the giant magnetoresistance element and the integrated circuit.
In a further preferred form of the invention, mean surface roughness of the underlayer is 50 xc3x85 or less.
In a further preferred form of the invention, mean surface roughness of the underlayer is between 1 xc3x85 and 25 xc3x85.
In a further preferred form of the invention, further comprising a differential amplifier and a comparator on a line for transmitting output of the giant magnetoresistance element to the integrated circuit, wherein the comparator sets the output of the differential amplifier being constant irrespective of the distance between the giant magnetoresistance element and the object to be observed by the giant magnetoresistance element, as the criterion for deciding the position of an object to be observed.
In accordance with a yet further aspect of the present invention, there is provided a magnetic field sensing device which comprises a magnetic rotating body being rotatable about the rotation axis and having a concavity and a convexity along its outer periphery, a magnet disposed so as to face the outer periphery of the magnetic rotating body and a magnetic field sensing element, which is attached to the magnet surface opposing the outer periphery of the magnetic rotating body, wherein the magnetic field sensing element detects a change in a magnetic field generated between the magnetic rotating body and the magnet during the rotation of the magnetic rotating body, and wherein the device detects a rotation amount of the magnetic rotating body on the basis of the detected change in the magnetic field.